“Our analysis suggests that MERS coronovirus does not yet have pandemic potential,” Romulus Breban, PhD, of the Emerging Diseases Epidemiology Unit at the Institut Pasteur in Paris, and colleagues reported in Lancet.

MERS shares many clinical, epidemiological and virological similarities to the severe acute respiratory syndrome (SARS) coronavirus, such as airborne transmission and high case-fatality ratio." So the researchers set out to compare the new cornavirus' prepandemic data with that of SARS.

They analyzed data from from WHO and 64 laboratory-confirmed cases of MERS available as of June 21, 2013. Patient age ranged from 2 to 94 years and 74% were male. The case-fatality ratio was 59.4% overall.

Using this data the researchers estimated the basic reproduction number (R0) -- or the number of secondary cases each index patient is expected to infect in a population -- for best- and worst-case scenarios. A virus is considered to have pandemic potential if its R0 exceeds 1.

In the best-case scenario, the MERS CoV R0 was 0.60 and reached 0.69 in the worst-case scenario. In comparison, the estimated R0 for SARS was 0.80, whereas the actual R0 for clinical SARS exceeded 2.

In worst-case estimates, eight or more secondary MERS infections caused by the next index patient would translate into a 5% or higher chance that the revised MER R0 would exceed 1. The researchers found this possibility “unlikely because the largest count of secondary cases attributed to a patient is seven (six in a dialysis ward and one outside) and is an outlier."

"MERS has not spread as rapidly or as widely as SARS did. SARS' adaption to humans took just several months, whereas MERS has already been circulating more than a year in human populations without mutating into a pandemic form," the researchers wrote.

However, these findings do not dismiss worldwide threat MERS-CoV poses, they cautioned. Despite the similarities between MERS and SARS, “the two viruses have distinct biology, such as the use of different receptors to infect cells in human airways." Therefore, comparisons of R0 figures do not provide a definitive conclusion about the pandemic potential for MERS-CoV.

Furthermore, the study's numbers may not be entirely representative, the researchers noted, as clinical intervention can may limit the natural course of the virus.

"When active contact tracing is operational, public health authorities might immediately stop viral transmission after the index patient has been diagnosed, and thus the available data would be just the number of secondary cases of the index patient before their isolation," the researchers explained.

Patients with less severe symptoms may also have been overlooked, while certain dynamics of population movement might alter the course of MERS transmission -- for example, millions of Muslims will arrive in Saudi Arabia during the Hajj in October.

Because of these factors, the researchers continued to emphasize the need for more research and continued efforts to control the spread of the virus.

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